Subdivision Surface not making things smooth as they are in the tutorial I am following
You need to delete the bottom face. Select it and press "X" and select "Faces" from the dropdown menu.



After you delete the bottom face an additional problem for your Modifiers/mesh occurs.

Set the "view" and "render" to 2 in the Sub Surf Modifier. 



In Edit Mode select all of the vertices and press "G" "Y" to move them slightly away from the center on the Y axis. 



Then check the box next to "Clipping" in the Mirror Modifier. Then "G" "Y" again and move all of your vertices back toward the center.